Symptomatic chikungunya and chronic post-infection arthralgia in a highly endemic setting in Northeastern Brazil, 2018–2019: Clinical characteristics, prevalence and associated factors

Chikungunya, an Aedes-borne disease, poses a significant global health threat due to its substantial morbidity. The prevalence of symptomatic chikungunya virus (CHIKV) infection and chronic arthralgia, as well as their associated factors, vary geographically and across studies. We estimated the prevalence of these outcomes in a household-based survey conducted in a large northeastern Brazilian city (2018-2019) approximately three years after the city's first CHIKV outbreak (2016). Sociodemographic and clinical data were collected through interviews, and arboviruses serostatus (IgG and/or IgM) was determined using ELISA. Arthralgia severity was assessed via Visual Analog Scale (VAS). Prevalence estimates (95% CI) and adjusted prevalence ratios (aPRs) were estimated using Poisson regression with robust variance. Principal Component Analysis (PCA) was used to address multicollinearity and identify latent risk profiles . Of the 760 CHIKV-exposed participants, 70% (95% CI: 66.7-73.2; n = 532) reported symptomatic infections. Among those reporting arthralgia (n = 499), 36.5% (95% CI: 32.4-40.8) experienced symptoms lasting >90 days, and of these, over 70% reported severe pain (VAS ≥ 8). In multivariable analyses, older age (aPR = 1.21 [36-50 years], aPR = 1.19 [51-65 years]), female sex (aPR = 1.19; 95% CI: 1.08-1.32), and prior DENV exposure (aPR = 1.45; 95% CI: 1.03-2.04) were associated with - symptomatic infection, whereas higher income showed a protective association. PCA confirmed these formed distinct risk profiles; a sociodemographic component (older age, prior DENV and single marital status) and a biological sex component each independently increased the odds of symptomatic disease by 31% (aOR=1.31). For chronic arthralgia, risk increased with older age (aPR = 4.60 [51-65 years]), female sex (aPR = 1.70; 95% CI: 1.29-2.25), and severe acute pain (aPR = 2.91; 95% CI: 1.86-4.55), but inversely associated with low income (aPR = 0.67). These findings underscore the need for targeted interventions, particularly for older adults, women, and low-income groups. Further studies are needed to elucidate the immunological mechanisms underlying these associations.